Optical viewing systems of various designs exist to modify optical images that pass through those systems. For example, some augmented reality systems incorporate optical systems that allow selective removal of portions of an image of a scene being viewed by a user through the optical system. One example of such optical systems uses a head mounted display that has one optical path or a pair of optical paths with one optical path for each eye. Operations upon the light passing through the one or more optical paths are able to create optical effects, including blockage of portions of the image being viewed. These optical effects are able to create an augmented reality experience. An example of such image processing includes processing that is able to block out part of an image entering the optical path, add visual content to the viewed image at an output of the optical path, or both.
Existing augmented reality systems present various trade-offs. For example, head mounted displays tend to be thick in order to incorporate the components that make up their optical paths. A head mounted display that incorporates a “see-through” optical path, i.e., an optical path that allows optical images to pass through the optical path of the system, are able to obstruct a portion of the image being viewed, but such obstructions appear to be “blurry” and precise delimiting of the blockage in the observer's sight is not possible. Because such head mounted displays contain the optical paths with the light blocking components and the head mounted display is mounted in close proximity to the wearer's eyes, the light blocking components are not in focus and therefore cannot sharply block portions of the image being viewed.
In general, the images produced by augmented reality systems are presented to an observer so as to appear to be located at a distance of between two meters and infinity in front of the observer. In an example, images created by such displays are able to be added to actual physical scenes being viewed by the observer. The fixed perceived distance of the presented images limit the ability of these presented images to be mixed with or otherwise augment actual physical scenes being viewed by the observer.
Three-dimensional head mounted displays present auto-stereoscopic images by presenting slightly different images to each eye of an observer. These images are presented by, for example, an LCD display that an observer sees by looking through an optical system of the head mounted display. One aspect of autostereoscopic displays is that each image contains picture elements that are located in the image with location offsets relative to a corresponding picture element in the image presented to the other eye. The different locations of these corresponding picture elements simulate the different angles of arrival of light rays at each of an observer's two eyes from real objects that are located at various distances from the observer.
Such autostereoscopic displays simulate the differences in angle of arrival at each eye due to the simulated distance of a particular object from the observer. When perceiving real objects at various distances, however, the two human eyes perceive not only the difference in angle of arrival of light from a particular object, but the brain further adjusts the lens of each eye to optically bring into focus different objects that are located at different distances from the eye. The human brain detects distance based not only upon different angles of arrival of light form objects at different distances, but also based upon distances that corresponds to the adjustments to the eye's lens that are required to bring the object into focus.
Although conventional autostereoscopic systems accurately simulate the different angle of arrival of light rays from objects at different simulated distances, each eye is still presented with one image containing elements that are all focused by the eye's lens as being at the same distance in front of the eye. In other words, the eye's lens focuses upon all elements of its respective image and all of those elements appear to be located at one distance from the eye—at the perceived distance of the presented image. The operation of such systems presents the brain with inconsistent distance information, the difference in apparent angle of arrival of light from an object does not correspond to the distance of the object that corresponds to the focused distance of the object perceived by the eye's lens. Thus inconsistent distance information presented to the brain sometimes causes a person who is viewing simulated three-dimensional images through an autostereoscopic system to experience headaches or other discomfort.
Therefore, the effectiveness of image modifying optical systems is limited by presenting an observer with images of selectable light blocking components and real images being augmented that appear at different distances from the observer, and are thereby not able to be simultaneously in focus.